It's a sound they don't want to hear in Makiki. So, as they walked around they listened for coqui. It's part of the evening's effort to get more people involved in locating the invasive species on Oahu.

"These frogs can be anywhere and we're a small organization so we need their help to tell us where the frogs are," said Rachel Neville from the Oahu Invasive Species Committee.

Along with listening, Case also used the Honolulu 311 app to let the experts know this part of Makiki was all clear.

"I know that sending in information whether you hear or not, helps to map it out," said Case.

But the effort to stop the invasive species doesn't end. More work must be done to keep the tiny frogs from spreading.

"Because the Big Island is so infested, the frogs can come over in anything that has enough water so they can survive the journey," said Neville.

Twenty pests were captured this year alone, and these small amphibians with the big call have ended up all over the island.

"We've found them in Mililani, Leeward side, North Shore, East Honolulu, Windward side; removed from all these places," said Neville.

Now if you do hear a coqui, grab your smartphone and use the free Honolulu 311 app on iPhone, Android, and Windows Phone to record it and let the experts know where to find it.

"By the time frogs get really loud, and people lose sleep it's too late to do anything about it," said Neville.

The coqui came from Puerto Rico to Hawaii. But here, it has no natural predators to keep populations in check. The loud sound from the coqui is the mating call of the male frogs.